1. Technical Field of the Invention
The present invention relates to a reflection-type light modulating array element and an exposure apparatus.
2. Description of the Related Art
The spatial light modulator (SLM) is a device of modulating incident light of a spatial pattern and forming an optical image corresponding to the electrical or optical input. One of SLM is a digital micromirror device (DMD) where a micromirror is produced based on the micromechanic technology and light is deflected by inclining the micromirror. DMD is a monolithic single-chip integrated circuit SLM and comprises, for example, a high-density array of about 16 micron-square movable micromirrors. These mirrors are fabricated over an address circuit and each mirror forms one pixel of the DMD array. This mirror reflects incident light to a projection lens in one of two positions and deflects the incident light to a light absorber in another position. The projection lens focuses the modulated light on a display screen to form an image.
The spatial light modulator 1 disclosed in JP-A-8-334709 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) has, as shown in FIG. 25A, a square mirror 7 entirely supported on and elevated above a yoke 5 by a support post 3. The support post 3 extending downward from the center of the mirror 7 is, as shown in the Figure, fixed along its torsion axis to the center of the yoke 5 and balances the center of mass of the mirror 7 on the yoke 5. When the yoke 5 and the mirror 7 are in the undeflected (flat) state, the yoke 7 is entirely coplanar with the elevated address electrodes 9 and 11 at a distance of about 1 μm above the metal layer including address electrodes 13 and 15 and reset/bias 17. The mirror 7 is elevated above the pair of elevated address electrodes 9 and 11 about 2 μm which is approximately double the distance separating the yoke 5 from the substrate 19.
In this spatial light modulator 1, when a voltage is applied between the mirror 7 and the elevated address electrode 11 and between the yoke 5 and the lower address electrode 15, the electrostatic force generated between respective electrodes causes, as shown in FIG. 25B, the yoke 5 and the mirror 7 to rotate clockwise, and one landing tip 21 of the yoke 5 lands on the lower address electrode 15. According to the electrodes to which a voltage is applied, free rotation to both the left and right directions can be attained.
The light deflecting apparatus 25 disclosed in JP-A-2000-214397 comprises, as shown in FIG. 26A, a deflecting plate 27 having a deflecting plane for deflecting an incident light beam, at least one flexible plate 33 connected at one end to the deflecting plate 27 and at the other end to supporting substrates 29 and 31, and a unit of fixed electrode 35 and driving electrode 37 for displacing the deflecting plate 27. The unit of fixed electrode 35 and driving electrode 37 is consisting of a movable portion (driving electrode 37) provided on the flexible plate 33, and fixed electrodes 35 formed on the sides of supporting substrates 29 and 31, where the flexible plate 33 is driven by the attractive force generated between the driving electrode 37 and the fixed electrode 35 to cause displacement of the deflecting plate 27.
In this light deflecting apparatus 25, when a voltage is applied between the fixed electrode 35 and the driving electrode 37 provided on the flexible plate 33, an electrostatic attractive force is generated between two electrodes 35 and 37. By this electrostatic force, the flexible plate 33 is attracted upward or downward with respect to a substrate 39 for the formation of electrode, as a result, the deflecting plate 27 is, as shown in FIG. 26B, tilted and displaced. For returning the flexible plate 33 to the state of FIG. 26A, an appropriate voltage is applied between the driving electrode 37 and the fixed electrode 35 on the upper side or between the driving electrode 37 and the fixed electrode 35 on the lower side to return the flexible plate 33 to the center position and thereafter, the voltage is turned off.
In the light deflecting apparatus 41 disclosed in Dual-Mode Micromirrors for Optical Phased Array Applications, TRANSDUCERS 01 EUROSENSORS XV (The 11th International Conference on Solid-Sensors and Actuators (2001)), as shown in FIG. 27, a mirror 45 is supported in the center portion of a rocking axis 43, and support axes 47 and 47 are fixed to both ends of the rocking axis 43 in an orthogonal manner. In each of these support axes 47 and 47, a so-called comb drive 49 as driving means is provided at both ends. The comb drive 49 is oriented by alternately inserting a comb teeth-like upper electrode plate 49a and a comb teeth-like lower electrode 49b and due to the electrostatic force generated between these opposing electrodes, both ends of each of the support axes 47 and 47 are moved up and down, as a result, the rocking axis 43 is rotated and thereby the mirror 43 can be rotated freely in both the left and right directions.
However, in the spatial light modulator disclosed in JP-A-8-334709, a two-step structure consisting of a yoke part taking a driving role and a mirror part having an area enlarged with respect to the yoke part is constituted on a torsion hinge so as to obtain a high opening ratio for one pixel mirror of a fine area and therefore, the mass of the entire movable part becomes large, as a result, the moment of inertia is increased and high-speed moving is limited. Furthermore, since the elevated address electrodes and the yoke are coplanarly disposed, the area of each electrode is decreased to give a small electrostatic force both between the pixel mirror and the elevated address electrode and between the yoke and the lower address electrode, and low-voltage and high-speed driving is limited.
In the light deflecting apparatus disclosed in JP-A-2000-214397, the support member (flexible plate) is drawn upward or downward upon displacement of the deflecting plate to cause dogleg bending of the linking part between the flexible plate and the deflecting plate and this gives rise to increase in distortion and reduction in durability.
In the light deflecting apparatus disclosed in Dual-Mode Micromirrors for Optical Phased Array Applications, TRANSDUCERS 01 EUROSENSORS XV, not only the comb drive structure is complicated but also four comb drives are necessary and therefore, a large area is occupied by the drive structure to cause problems that miniaturization and high resolution are difficult to realize and the utility efficiency of light is bad.